I have an 8g with a betta, 2 mystery snails and 3 shrimp. I actually really love this tank because its occupants are either really pretty or really interesting and I have it well planted but, I have to do water changes every couple of days because the snails poop a lot. Other than that everyone gets along really well.

I'm ready for the pressure.
The drama and the pleasure!If there is one thing I want to see here, it's HUMOR.I believe I can fly!
I believe I can touch the sky!
I think about it every night and day!I stand in awe of my body.

My smallest is a 2.5 gal. I'm having lots of issues with the ammonia so nothing is in the now. I plan to eventually put in a malle betta and I have either mtsnails of some ramshorn snail that i can put in there. As it's currently empty, I'll also list me next smallest :)
10 gal with cherry shrimp, dwarf frogs, fancy guppies (use some babies as feeds in other tanks), and one male betta that I just put in and am watching closely for any aggression but I have seen none. This tank is heavily plantsed also with java moss, hygrophilia difformis, duckweed, a crispos, cambomba, and a few unknows that i got for free. I think with all the view breakups, it helps the betta ignore the fins of the guppies.